"There was nobody out there for me to look at and say maybe this is unhealthy," Lovato, who battled eating disorders, says on an episode of the The Ellen DeGeneres Show scheduled to air Tuesday. "I want to be that for a 13-year old girl at home deciding whether or not to eat dinner, or an 18-year-old girl deciding whether or not to keep her breakfast down."

When the singer-actress finished treatment in January, she wanted to be "outspoken" and freely talk about her "issues" because when she grew up, she "was dealing with the pressures to be thin."

"It was the time in the tabloids when very, very skinny girls were on the cover of every magazine, and that's what I was looking up to," she says. "That's what I had to idolize. I don't want that for young girls to idolize."

Although she calls her life pre-treatment a "mess," she's actually grateful for her "meltdown."

"So many things were going great in my life, and then all of a sudden my personal life just went down at crazy speeds," she says. "I had a negative breakdown and it changed my life forever."